Raspberry Pi 3 function mode matrix

The following modes in each table are mutually exclusive on the Raspberry Pi
3.

UART modes

The Raspberry Pi has a single full-speed UART (UART0) and a mini UART
(MINIUART); see the official docs
for information on their differences. These UARTs are multiplexed
between various board functions and cannot be used simultaneously. The following
modes are supported:

Note: Switching back to Audio mode requires a device reboot due to
limitations of the hardware.

When you are creating a hardware configuration in the
Android Things Console, BCM18 and BCM19
pullup and pulldown resistors don't apply until the GPIO is actually
opened in order to avoid interfering with the I2S bus on the same pins.